1. Field of the Invention
The present invention relates to a manufacturing method of a magnetic recording medium including a recording layer having a concavo-convex pattern.
2. Description of the Related Art
Conventionally, in a magnetic recording medium such as a hard disk, various types of development such as miniaturization of magnetic particles forming a recording layer, change of a material, and finer head processing have been made to largely improve areal density of the recording layer. The improvement of the areal density is expected to continue. However, many problems including the limitation of the magnetic head processing, improper recording of information onto a track adjacent to a target track and crosstalk that are caused by broadening of a magnetic field, and the like have been made apparent. Thus, the improvement of the areal density by the conventional development approach has reached the limit.
Therefore, a magnetic recording medium such as a discrete track medium and a patterned medium, that includes a recording layer formed in a predetermined concavo-convex pattern in which recording elements form convex portions, has been proposed as a candidate of a magnetic recording medium that enables further improvement of the areal density.
On the other hand, a magnetic recording medium such as a hard disk has a problem that a flying height of a head slider is unstable in a case where concavity and convexity of a surface is large. Thus, a magnetic recording medium has been proposed in which concave portions between recording elements are filled with a filling material so as to flatten a surface of a recording layer (see Japanese Patent Laid-Open Publication No. 2000-195042, for example).
A method using a lift-off technique is known as a method for filling the concave portions of the recording layer having a concavo-convex pattern with the filling material so as to flatten the surface of the recording layer. An exemplary method is now described. First, a continuous recording layer and a resist layer are uniformly formed over a substrate. The resist layer in regions corresponding to the concave portions of the concavo-convex pattern is then removed by exposure and development, so that the resist layer covers portions of the continuous recording layer that correspond to the convex portions only. An exposed portion of the continuous recording layer is etched in that state, thereby forming the recording layer with the concavo-convex pattern formed therein. Then, the filling material is deposited on the recording layer and the resist layer so as to fill the concave portions of the recording layer with the filling material. The filling material is formed to have a concavo-convex pattern following the concavo-convex pattern of the recording layer and is also deposited on the resist layer. Finally, the resist layer is dissolved using an organic solvent so as to be removed together with the filling material formed thereon. In this manner, the filling material is left in the concave portions only and the surface of the recording layer is flattened (see Japanese Patent Publication No. Hei 5-22291 and Japanese Patent Laid-Open Publication No. 2001-110050, for example).
However, the filling material is also deposited on side faces of the resist layer. The thus deposited part of the filling material may remain while being integrated with the filling material in the concave portion, after removal of the resist layer. In other words, the filling material is used for filling the concave portions of the concavo-convex pattern and may also form a projection near an end of the concave portion. In this case, the surface of the recording layer is not flattened sufficiently.
If the resist layer is formed to be excessively thick, formation of the projection can be suppressed because it is difficult for the filling material to be deposited around the base of the side face of the resist layer. However, the excessively thick resist layer may cause easy destruction of the convex portion of the resist layer that is processed to have a concavo-convex pattern by exposure and development or may lower processing accuracy of the recording layer.